pretty-print JSON using JavaScript

Question

How can I display JSON in an easy-to-read (for human readers) format? I\'m looking primarily for indentation and whitespace, with perhaps even colors / font-styles / etc.

Answer 1

If you're looking for a nice library to prettify json on a web page...

Prism.js is pretty good.

http://prismjs.com/

I found using JSON.stringify(obj, undefined, 2) to get the indentation, and then using prism to add a theme was a good approach.

If you're loading in JSON via an ajax call, then you can run one of Prism's utility methods to prettify

For example:

Prism.highlightAll()

Answer 2

For debugging purpose I use:

console.debug("%o", data);

• https://getfirebug.com/wiki/index.php/Console_API
• https://developer.mozilla.org/en-US/docs/DOM/console

Answer 3

It works well:

console.table()

Read more here: https://developer.mozilla.org/pt-BR/docs/Web/API/Console/table

Answer 4

Based on Pumbaa80's answer I have modified the code to use the console.log colours (working on Chrome for sure) and not HTML. Output can be seen inside console. You can edit the _variables inside the function adding some more styling.

function JSONstringify(json) {
    if (typeof json != 'string') {
        json = JSON.stringify(json, undefined, '\t');
    }

    var 
        arr = [],
        _string = 'color:green',
        _number = 'color:darkorange',
        _boolean = 'color:blue',
        _null = 'color:magenta',
        _key = 'color:red';

    json = json.replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {
        var style = _number;
        if (/^"/.test(match)) {
            if (/:$/.test(match)) {
                style = _key;
            } else {
                style = _string;
            }
        } else if (/true|false/.test(match)) {
            style = _boolean;
        } else if (/null/.test(match)) {
            style = _null;
        }
        arr.push(style);
        arr.push('');
        return '%c' + match + '%c';
    });

    arr.unshift(json);

    console.log.apply(console, arr);
}

Here is a bookmarklet you can use:

javascript:function JSONstringify(json) {if (typeof json != 'string') {json = JSON.stringify(json, undefined, '\t');}var arr = [],_string = 'color:green',_number = 'color:darkorange',_boolean = 'color:blue',_null = 'color:magenta',_key = 'color:red';json = json.replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {var style = _number;if (/^"/.test(match)) {if (/:$/.test(match)) {style = _key;} else {style = _string;}} else if (/true|false/.test(match)) {style = _boolean;} else if (/null/.test(match)) {style = _null;}arr.push(style);arr.push('');return '%c' + match + '%c';});arr.unshift(json);console.log.apply(console, arr);};void(0);

Usage:

var obj = {a:1, 'b':'foo', c:[false,null, {d:{e:1.3e5}}]};
JSONstringify(obj);

Edit: I just tried to escape the % symbol with this line, after the variables declaration:

json = json.replace(/%/g, '%%');

But I find out that Chrome is not supporting % escaping in the console. Strange... Maybe this will work in the future.

Cheers!

Answer 5

<!-- here is a complete example pretty print with more space between lines-->
<!-- be sure to pass a json string not a json object -->
<!-- use line-height to increase or decrease spacing between json lines -->

<style  type="text/css">
.preJsonTxt{
  font-size: 18px;
  text-overflow: ellipsis;
  overflow: hidden;
  line-height: 200%;
}
.boxedIn{
  border: 1px solid black;
  margin: 20px;
  padding: 20px;
}
</style>

<div class="boxedIn">
    <h3>Configuration Parameters</h3>
    <pre id="jsonCfgParams" class="preJsonTxt">{{ cfgParams }}</pre>
</div>

<script language="JavaScript">
$( document ).ready(function()
{
     $(formatJson);

     <!-- this will do a pretty print on the json cfg params      -->
     function formatJson() {
         var element = $("#jsonCfgParams");
         var obj = JSON.parse(element.text());
        element.html(JSON.stringify(obj, undefined, 2));
     }
});
</script>

Answer 6

Unsatisfied with other pretty printers for Ruby, I wrote my own (NeatJSON) and then ported it to JavaScript including a free online formatter. The code is free under MIT license (quite permissive).

Features (all optional):

• Set a line width and wrap in a way that keeps objects and arrays on the same line when they fit, wrapping one value per line when they don't.
• Sort object keys if you like.
• Align object keys (line up the colons).
• Format floating point numbers to specific number of decimals, without messing up the integers.
• 'Short' wrapping mode puts opening and closing brackets/braces on the same line as values, providing a format that some prefer.
• Granular control over spacing for arrays and objects, between brackets, before/after colons and commas.
• Function is made available to both web browsers and Node.js.

I'll copy the source code here so that this is not just a link to a library, but I encourage you to go to the GitHub project page, as that will be kept up-to-date and the code below will not.

(function(exports){
exports.neatJSON = neatJSON;

function neatJSON(value,opts){
  opts = opts || {}
  if (!('wrap'          in opts)) opts.wrap = 80;
  if (opts.wrap==true) opts.wrap = -1;
  if (!('indent'        in opts)) opts.indent = '  ';
  if (!('arrayPadding'  in opts)) opts.arrayPadding  = ('padding' in opts) ? opts.padding : 0;
  if (!('objectPadding' in opts)) opts.objectPadding = ('padding' in opts) ? opts.padding : 0;
  if (!('afterComma'    in opts)) opts.afterComma    = ('aroundComma' in opts) ? opts.aroundComma : 0;
  if (!('beforeComma'   in opts)) opts.beforeComma   = ('aroundComma' in opts) ? opts.aroundComma : 0;
  if (!('afterColon'    in opts)) opts.afterColon    = ('aroundColon' in opts) ? opts.aroundColon : 0;
  if (!('beforeColon'   in opts)) opts.beforeColon   = ('aroundColon' in opts) ? opts.aroundColon : 0;

  var apad  = repeat(' ',opts.arrayPadding),
      opad  = repeat(' ',opts.objectPadding),
      comma = repeat(' ',opts.beforeComma)+','+repeat(' ',opts.afterComma),
      colon = repeat(' ',opts.beforeColon)+':'+repeat(' ',opts.afterColon);

  return build(value,'');

  function build(o,indent){
    if (o===null || o===undefined) return indent+'null';
    else{
      switch(o.constructor){
        case Number:
          var isFloat = (o === +o && o !== (o|0));
          return indent + ((isFloat && ('decimals' in opts)) ? o.toFixed(opts.decimals) : (o+''));

        case Array:
          var pieces  = o.map(function(v){ return build(v,'') });
          var oneLine = indent+'['+apad+pieces.join(comma)+apad+']';
          if (opts.wrap===false || oneLine.length<=opts.wrap) return oneLine;
          if (opts.short){
            var indent2 = indent+' '+apad;
            pieces = o.map(function(v){ return build(v,indent2) });
            pieces[0] = pieces[0].replace(indent2,indent+'['+apad);
            pieces[pieces.length-1] = pieces[pieces.length-1]+apad+']';
            return pieces.join(',\n');
          }else{
            var indent2 = indent+opts.indent;
            return indent+'[\n'+o.map(function(v){ return build(v,indent2) }).join(',\n')+'\n'+indent+']';
          }

        case Object:
          var keyvals=[],i=0;
          for (var k in o) keyvals[i++] = [JSON.stringify(k), build(o[k],'')];
          if (opts.sorted) keyvals = keyvals.sort(function(kv1,kv2){ kv1=kv1[0]; kv2=kv2[0]; return kv1<kv2?-1:kv1>kv2?1:0 });
          keyvals = keyvals.map(function(kv){ return kv.join(colon) }).join(comma);
          var oneLine = indent+"{"+opad+keyvals+opad+"}";
          if (opts.wrap===false || oneLine.length<opts.wrap) return oneLine;
          if (opts.short){
            var keyvals=[],i=0;
            for (var k in o) keyvals[i++] = [indent+' '+opad+JSON.stringify(k),o[k]];
            if (opts.sorted) keyvals = keyvals.sort(function(kv1,kv2){ kv1=kv1[0]; kv2=kv2[0]; return kv1<kv2?-1:kv1>kv2?1:0 });
            keyvals[0][0] = keyvals[0][0].replace(indent+' ',indent+'{');
            if (opts.aligned){
              var longest = 0;
              for (var i=keyvals.length;i--;) if (keyvals[i][0].length>longest) longest = keyvals[i][0].length;
              var padding = repeat(' ',longest);
              for (var i=keyvals.length;i--;) keyvals[i][0] = padRight(padding,keyvals[i][0]);
            }
            for (var i=keyvals.length;i--;){
              var k=keyvals[i][0], v=keyvals[i][1];
              var indent2 = repeat(' ',(k+colon).length);
              var oneLine = k+colon+build(v,'');
              keyvals[i] = (opts.wrap===false || oneLine.length<=opts.wrap || !v || typeof v!="object") ? oneLine : (k+colon+build(v,indent2).replace(/^\s+/,''));
            }
            return keyvals.join(',\n') + opad + '}';
          }else{
            var keyvals=[],i=0;
            for (var k in o) keyvals[i++] = [indent+opts.indent+JSON.stringify(k),o[k]];
            if (opts.sorted) keyvals = keyvals.sort(function(kv1,kv2){ kv1=kv1[0]; kv2=kv2[0]; return kv1<kv2?-1:kv1>kv2?1:0 });
            if (opts.aligned){
              var longest = 0;
              for (var i=keyvals.length;i--;) if (keyvals[i][0].length>longest) longest = keyvals[i][0].length;
              var padding = repeat(' ',longest);
              for (var i=keyvals.length;i--;) keyvals[i][0] = padRight(padding,keyvals[i][0]);
            }
            var indent2 = indent+opts.indent;
            for (var i=keyvals.length;i--;){
              var k=keyvals[i][0], v=keyvals[i][1];
              var oneLine = k+colon+build(v,'');
              keyvals[i] = (opts.wrap===false || oneLine.length<=opts.wrap || !v || typeof v!="object") ? oneLine : (k+colon+build(v,indent2).replace(/^\s+/,''));
            }
            return indent+'{\n'+keyvals.join(',\n')+'\n'+indent+'}'
          }

        default:
          return indent+JSON.stringify(o);
      }
    }
  }

  function repeat(str,times){ // http://stackoverflow.com/a/17800645/405017
    var result = '';
    while(true){
      if (times & 1) result += str;
      times >>= 1;
      if (times) str += str;
      else break;
    }
    return result;
  }
  function padRight(pad, str){
    return (str + pad).substring(0, pad.length);
  }
}
neatJSON.version = "0.5";

})(typeof exports === 'undefined' ? this : exports);